1. Field of the Invention
The present invention relates to rigid cellular foam compositions. More particularly, the present invention relates to rigid cellular foams characterized by carbodiimide linkages. Even more particularly, the present invention pertains to rigid cellular foams characterized by carbodiimide linkages which are prepared from toluene diisocyanate-rich isocyanates.
2. Prior Art
There have been disclosed heretofore a plurality of means and methods for the preparation of rigid cellular foams characterized by carbodiimide linkages. Generally speaking, the prior art teaches the use of varying catalytic systems for initiating the isocyanate condensation reaction which characterizes the mode of preparation of these cellular products. Other prior art references teach the incorporation of various additives for altering the physical properties of the resultant foams. Thus, the prior art teaches, in this respect, the use of surfactants, blowing agents, and the like.
Exemplifying the prior art under consideration are U.S. Pat. Nos. 3,645,923; 3,806,475; 3,772,217; 3,766,103; 3,748,289; 3,732,187, etc.
However, it will be gleaned from a review of the prior art, that in instances of preparation of the present foam compositions crude methylene diphenyl diisocyanate has been the sole or major isocyanate component. The use of pure toluene diisocyanate as the sole, or major isocyanate component, on the other hand is unknown. This is because conventional one-shot foaming reactions, substituting distilled toluene diisocyanate for crude methylene diphenyl diisocyanate, provides foams which are extremely friable and very low in compressive strength. Furthermore, the inclusion of polyols into distilled toluene diisocyanate systems does not overcome the problem of friability as it does with crude methylene diphenyl diisocyanate.
The present invention, on the other hand, provides an salient solution to the problem of utilizing distilled toluene diisocyanate as the major isocyanate component in the preparation of the foams of the type under consideration.